Description of the Hollidaysburg and Huntingdon Quadrangles
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DESCRIPTION OF THE HOLLIDAYSBURG AND HUNTINGDON QUADRANGLES By Charles Butts INTRODUCTION 1 BLUE RIDGE PROVINCE topography are therefore prominent ridges separated by deep SITUATION The Blue Ridge province, narrow at its north end in valleys, all trending northeastward. The Hollidaysburg and Huntingdon quadrangles are adjoin Virginia and Pennsylvania, is over 60 miles wide in North RELIEF ing areas in the south-central part of Pennsylvania, in Blair, Carolina. It is a rugged region of hills and ridges and deep, The lowest point in the quadrangles is at Huntingdon, Bedford, and Huntingdon Counties. (See fig. 1.) Taken as narrow valleys. The altitude of the higher summits in Vir where the altitude of the river bed is about 610 feet above sea ginia is 3,000 to 5,700 feet, and in western North Carolina 79 level, and the highest point is the southern extremity of Brush Mount Mitchell, 6,711 feet high, is the highest point east of Mountain, north of Hollidaysburg, which is 2,520 feet above the Mississippi River. Throughout its extent this province sea level. The extreme relief is thus 1,910 feet. The Alle stands up conspicuously above the bordering provinces, from gheny Front and Dunning, Short, Loop, Lock, Tussey, Ter each of which it is separated by a steep, broken, rugged front race, and Broadtop Mountains rise boldly 800 to 1,500 feet from 1,000 to 3,000 feet high. In Pennsylvania, however, above the valley bottoms in a distance of 1 to 2 miles and are South Mountain, the northeast end of the Blue Ridge, is less the dominating features of the landscape. The relief in the prominent. The rocks of this province are closely folded broad intervening valleys ranges from 100 to 600 feet but is quartzite, slate, schist, gneiss, granite, and greenstone. generally 200 to 300 feet. VALLEY AND RIDGE PROVINCE 2 PRINCIPAL TOPOGRAPHIC FEATURES The Valley and Ridge province is a belt of country 50 to 80 The Allegheny Front, generally known as Allegheny Moun miles wide extending from New York to Alabama in a general tain, the great eastward-facing escarpment of the Appalachian direction about S. 40° W. and bounded by the Blue Ridge on Plateaus, is the most impressive feature of these quadrangles. the southeast and the Appalachian Plateaus on the northwest. It crosses the west side of the Hollidaysburg quadrangle and This belt is characterized by broad valleys separated by high rises to a height of 3,136 feet above sea level in Blue Knob, in ridges trending parallel with the belt. These ridges, however, the southeast corner of the adjoining Ebensburg quadrangle are grouped more along the northwest half of the valley, leav (pi. 1). The eastern foothills of this escarpment descend to a 77" 76° ing a broader valley on the southeast side known as the valley continuous with Bald Eagle Valley on the northeast and FIGURE 1. Index map of south-central Pennsylvania and parts of Cumberland Valley in Pennsylvania and the Shenandoah with the valley of Frankstown Branch on the southwest. adjacent States. Valley or the Valley of Virginia on the southeast side of the From a point opposite Hollidaysburg through Altoona this The location of the Hollidaysburg and Huntingdon quadrangles is shown by darker ruling (No. 327). Published folios describing other quadrangles are indicated by lighter ruling belt. In Pennsylvania the Allegheny Front, which bounds valley is known as Logan Valley. Nearly inclosed by Brush, and are listed on the back cover of this folio. the Valley and Ridge province on the west, rises from 1,000 Lock, Loop, and Short Mountains is a deep topographic a unit they are bounded by parallels 40°15' and 40°30' and to 1,500 feet above the main valley levels, but only its highest depression known as Scotch Valley. Point View knob in meridians 78° and 78°30'. Each quadrangle includes one- knobs rise much above the highest of the valley ridges. Blue the northwest corner of the Huntingdon quadrangle is another sixteenth of a "square degree" of the earth's surface, and its Knob, on the Allegheny Front, in the northern part of Bed striking topographic feature (pi. 2). The broad lowland area is approximately 228 square miles. These quadrangles ford County, stands 3,136 feet above sea level and 1,500 feet between Lock and Dunning Mountains on the west and form a part of the Appalachian Highlands, which extend from above the surface of Nittany Valley. (See pi. 1.) South Tussey Mountain on the east, known as Morrisons Cove (pi. 3), the Atlantic Coastal Plain on the east to the Interior Plains on Mountain, on the southeast side of the Valley and Ridge is really a somewhat offset continuation of Nittany Valley, the west and from Canada to central Alabama. province, in Franklin, Adams, and Cumberland Counties rises Centre County. Raystown Valley is the broad, undulating, APPALACHIAN HIGHLANDS 1,000 feet above the valley level. Near Big Stone Gap, Va., relatively }ow land between Tussey and Terrace Mountains, the crest of Black Mountain is 3,000 feet above the valley on marked by northeastward-trending narrow ridges and drained SUBDIVISIONS the northwest side, and in northern Tennessee Holston by Raystown Branch of the Juniata River. Southeast of Differences in topography, rocks, and geologic structure Mountain, near the northwest front of the Blue Ridge province, Raystown Valley Terrace Mountain and Sideling Hill with form the basis for a natural division of the Appalachian High rises nearly 3,000 feet above the valley on the southeast side. the north end of Broad Top Mountain, which together inclose lands into several parts called provinces. These are, from These features are exhibited in the profile section of Figure 2. the Great Trough Creek Valley (pi. 4), are the principal southeast to northwest, the Piedmont province, the Blue Ridge The rocks in these quadrangles, as in the entire Valley and topographic features. province, the Valley and Ridge province, and the Appalachian Ridge province, are limestone, dolomite, conglomerate, sand All the great ridges are caused by hard sandstones which, Plateaus. The boundaries of these provinces are shown on stone, and shale, which have been greatly disturbed by folding with the exception of that forming the summit of the Alle Figure 2. West of the Appalachian Plateaus are the Interior and faulting. gheny Front, are steeply inclined. The softer shales and the APPALACHIAN PLATEAUS soluble limestones have been eroded away faster than the hard sandstones, which are left in high relief. The slopes of these The Appalachian Plateaus, which are practically coextensive ridges in places are more than 20°, as for example the east with the Appalachian coal fields, are relatively high, ranging slope of Loop Mountain near the middle, where there is a from 800 feet above sea level in parts of Alabama to more than descent of 1,200 feet in half a mile. About the middle of 4,500 feet in Pocahontas County, W. Va., whence they descend the southeast slope of Lock and Dunning Mountains and the through Pennsylvania to about 2,000 feet in western New northwest slope of Tussey Mountain is a series of flat-topped York. Sandstone, conglomerate, shale, and coal beds make spurs, which are formed by another hard sandstone cropping up most of the rocks of the Appalachian Plateaus. In con out at that level. The coincidence of these features of relief trast with those of the Valley and Ridge province the strata of with the outcrpps of the several hard sandstone formations is the plateau province have been but slightly disturbed from clearly displayed on the geologic maps. their original horizontal attitude. A notable feature of the ridges is their parallelism, which is TOPOGRAPHY due to the geologic structure. (See pi. 5.) All the ridges are essentially hogbacks, the Allegheny Front, Dunning Mountain, The Hollidaysburg and Huntingdon quadrangles lie in a and some minor ridges being on the west limb and Tussey and region of mature topography. The great limestone valley Terrace Mountains- on the east limb of the great Nittany arch. between Dunning and Tussey Mountains has advanced to the (See structure sections.) Sideling Hill is a hogback on the FIGURE 2. Map of the central part of the Appalachian Highlands stage of early old age, as shown by the complete adjustment of Jacks Mountain anticline, whose crest is just east of the showing its physiographic divisions. the drainage as to both the distribution of the streams and the southeast corner of the Huntingdon quadrangle. (See pi. 6.) Low Plateaus, which are included in the Interior Plains by gradation of their beds. The stream beds are nearly free from Dunning and Tussey Mountains and Sideling Hill are sym the United States Geological Survey but which in the opinion rock shoals and waterfalls, and uniform slopes prevail in them. metrical, having equal slopes on their two sides, owing to the of some, of whom the writer is one, should be included in the The extremes of relief are considerable, and there is a moderate erect attitude of the rocks; the Allegheny Front and Terrace Appalachian Highlands. degree of diversity in surface forms. The dependence of Mountain are unsymmetrical, having steep slopes facing the topography upon the lithologic character and the attitude of Nittany arch and low slopes facing in the opposite directions, PIEDMONT PKOVINCE the underlying strata is abundantly and strikingly illustrated. owing to the low dip of the strata in those directions. The Piedmont province is a rolling upland 1,100 feet above The quadrangles lie almost wholly in the Valley and Ridge Several deep gaps or notches through the high ridges are sea level at the east foot of the Blue Ridge and 500 feet or less province, in the belt of ridges along its west side.